1. Field of the Invention
The present invention relates to systems for controlling electrically powered apparatus, and, in particular, to a system which controls the mode of active operation of the apparatus.
2. Description of the Prior Art
It is desirable to control the operation of many types of electrically powered apparatus from a location remote from the apparatus. For example, many conventional surgical lights require manual switching of energizing power from one light source to another--either to achieve a change in the illumination pattern produced by the light or to energize an operable source upon failure of an energized source--by actuating a switch at the light head, the housing which contains and supports the light sources of the surgical light. If a person other than one of the members of the surgical team is provided to operate the surgical light at the light head, the already congested surgical area becomes even more congested. If a member of the normal surgical team is assigned the duty of operating the surgical light, that member's attention is periodically diverted from that member's normal duties to operate the light, with the possible degradation of overall performance by that member. Therefore, it is desirable to permit manual switching of energizing power from one source to another from a controller mounted at a location remote from the light head to permit its operation by a person other than a member of the normal surgical team and without adding to the congestion of the surgical area.
Further, it is highly desirable to provide electrical communication between tne controller and the apparatus along only two electrical conductors. Electrical communication along only two conductors is less bulky, less expensive and generates less electrical noise than communication systems requiring more than two conductors.
Electrical communication from a remotely located controller along only two conductors, of course, is common. However, known systems using only two conductors for electrical communication between the controller and the apparatus can switch the apparatus among only two relatively simple modes of operations, for example, remotely turning off or on electrical lights. Further, only one such mode--the mode in which the light is on--can be considered an active mode of operation. However, additional active modes of operation are often required. In the case of electrically operated surgical lights, the modes of active operation of the lights must ensure the continuous maintenance of proper illumination during the performance of surgical procedures. To ensure that illumination having an appropriate pattern is available during the performance of the procedure, surgical lights are provided with different types of light sources which provide different types of light patterns. The sources can be either different types of lamps or one type of lamp with multiple filaments, which create different types of illumination patterns. Further, the surgical light should provide an indication at the controller that a light source has failed to permit replacement of that source. With one exception, all systems known to applicants which employ only two electrical conductors between the controller and the surgical lights are incapable of providing the level of control--and, therefore, the active modes of operation identified briefly above--needed to meet the concerns presented by the performance of surgical procedures. Such known systems permit only energizing or de-energizing remotely a single set of lights in a surgical suite. Accordingly, the loss of a light source of a surgical light causes the degradation or total loss of lighting of the surgical site. The remaining system of which applicants are aware is described in
U.S. patent application Ser. No. 362,117, filed Mar. 26, 1982, which is owned by the assignee of the present application, that switches energizing power from one filament of a lamp to another by reversing the polarity of the voltage applied to the light head of the surgical light by the controller.
A further problem pertaining to surgical lighting arises upon failure of a light source. If an energized light source fails, a backup light source must be energized quickly. If a backup light source fails, it must be replaced immediately to ensure that backup lighting is available in the event that an energized source fails. Many conventional surgical lights include a lighting control system which permits manual switching at the light head of energizing power from a failed source to a backup source, which is commonly a source of the type which provides an illumination pattern different from those provided by the energized sources and by the failed source. Requiring manual switching of energizing power from a failed light source to an operable source presents the obvious disadvantage of temporary loss of illumination between the times of failure of the failed source and energization of the backup source. Further, applicants are not aware of any surgical lights which provide an indication that a backup light source has failed.
Therefore, there is a need for a system for controlling the mode of active operation of electrically powered apparatus having a controller mounted at a location remote from the apparatus which communicates with the apparatus over only two electrical conductors. Further, there exists a need for a lighting control system which automatically de-energizes a failed light source and energizes an operable source upon failure of an energized source. Further, there is a need for a control system which monitors the operability of a backup light source to ensure that the backup source is available upon failure of an energized source.